In a wireless communication system, wireless terminals communicate with a Public Switched Telephone Network (PSTN) through distributed base stations. Each base station covers a selected geographic region commonly referred to as a "cell". At the boundaries, cells often overlap such that multiple base stations cover some common geographic area. While in a common area, a wireless terminal may be serviced by any of the associated base stations. Thus, when a call is initiated in a common area, a Mobile Switching Center (MSC) connects the call to the base station that receives the strongest signal from the wireless terminal. In current systems, the MSC connects the call to this base station even if the wireless terminal is traveling away from the base station. This can lead to unwanted service interruptions.
As a wireless terminal moves between cells during a single call, the wireless system disconnects the call from a first base station and connects the call through a second base station. This is commonly referred to as a "hand-off". Current wireless systems monitor the power of a signal received from a wireless terminal to determine when to hand-off a call to a different base station. When the signal power falls below a selected level, the wireless system polls the neighboring base stations to measure the power of the signal from the wireless terminal. The wireless system connects the call to the base station that recorded the strongest signal from the wireless terminal. By basing the hand-off decision on signal power, current wireless systems often hand-off a call to a base station even if the wireless terminal is currently moving away from the base station. Ultimately, such an improper hand-off can also lead to service interruption and subscriber dissatisfaction.
The demand for wireless telephone service is increasing at a rapid rate. To increase the capacity of existing wireless systems, wireless service providers split cells to increase the effective frequency reuse in a given area. By thus splitting the existing cells, a wireless service provider increases the number of potential hand-offs required during a single call and also increases the number of overlapping areas covered by multiple base stations. Thus, the frequency of improper hand-offs and subscriber dissatisfaction are likely to also increase.